1. Field of the Invention
This invention relates to medical articles. More particularly, it is concerned with medical articles made of a polyvinyl chloride compound which has excellent properties such as maintaining functions of blood constituents during preservation.
2. Description of the Prior Art
It is well known that blood has autoprotecting activities and, when contacted with foreign surfaces other than the internal wall of blood vessels, is encountered with adhesion to the foreign surfaces and agglutination of thrombocytes and gellation of blood plasma, that is fibrin bridges. With prior-art blood bags, thrombocytes in the blood is agglutinated on the plastic surface, and thrombocytic agglutinating activity is reduced to approximately 60% in 6 hours after blood collection and further to approximately 40% in 24 hours. Therefore, it is desirable that preservation vessels or other medical articles made of plastics capable of preserving blood cells for a longer period of time, that is, those which are compatible with blood be developed in order to enable efficient use of thrombocyte preparations.
Presently, as the plastic vessels or other medical articles are widely used blood bags made of soft polyvinyl chloride compound because of its properties such as good workability and pliability, low permeability to water vapor and high heat resistance. The soft polyvinyl chloride compound contains, as a plasticizer, from 30 to 60% of phthalic esters such as di-2-ethylhexyl phthalate (called DOP hereinbelow). It is known that the phthalic ester which is highly migratory is dissoluted into blood plasma when the soft polyvinyl chloride compound is formed, for example, into a blood preservation vessel. It is reported that if phthalic esters are dissolved into blood plasma containing concentrated thrombocytes due to the above-mentioned property, reduction in the coagulability which is a function of the thrombocyte is caused [Nihon Yuketsu Gakkaishi (Journal of the Blood Transfusion Society of Japan) 28, 282 (1982)].
On the other hand, polyester plasticizers are used as the non-migratory plasticizer. It is well known, however, that the polyester plasticizers which are principally composed of aliphatic esters are in general inferior in such properties as water resistance and hydrolyzability to phthalic esters which contain phenyl group as the skeleton.